29 mai 2018

Engineer / Postdoc Position (12 – 18 months) - Thermo-optical characterization and stability assessment of solar selective absorber materials for concentrated solar receivers


Scientific context

Concentrated Solar Power (CSP) technologies harvest direct solar irradiation, concentrate it with mirrors and convert it into heat thanks to a solar receiver ran by a heat transfer fluid. This heat can be further converted into electricity via a thermodynamical cycle. On one hand, the receiver materials must be able to withstand extreme conditions during 25 to 30 years of operation, including concentrated solar flux, high temperatures (200 –1000°C) in vacuum or air, thermal cycling, thermal shocks, etc. On the other hand, they must possess suitable optical properties. High absorptance α in the solar region (0.3 – 2.5 μm) is mandatory to maximize the amount of absorbed solar energy. Ideally, low infrared thermal emittance ε is also sought for, to limit radiative thermal losses which increase strongly with temperature (Stefan-Boltzmann’s law σT4). If these two properties are met, the material is said to be spectrally selective. At mid-temperatures, very efficient metallic receivers covered with solar selective absorber coatings maintained in vacuum are commonly employed. At high temperatures in air (T > 600 – 700°C), bulk materials with high thermal stability must be used instead, as coatings become unstable. Below 800°C, superalloys (e.g. Inconel) covered with non-selective absorbing black paints are used.

Above 800°C, refractory ceramic materials are preferred. Silicon carbide (SiC) is the material commonly used for this application because of its high resistance to oxidation and good sunlight absorptance, and despite its high emittance, leading to a poor spectral selectivity. Transition metal carbides of column IV, and notably titanium carbide (TiC), possess low emittance compared to SiC. However, their major limitation is their low resistance to oxidation. To improve the spectral selectivity of SiC and the oxidation resistance of TiC, the ANR CARAPASS project (2016-2020) proposes to associate them in SiC-TiC nanocomposite structures. Pellets are fabricated by Spark Plasma Sintering of nanopowders by the project partners (ICSM Marcoule, SPCTS Limoges). In order to evaluate the potential of these materials as solar selective receivers, a thorough characterization of their thermo-optical properties and thermal/oxidation stability is carried out at PROMES laboratory (Processes, Materials, Solar Energy), which specializes in CSP technologies and thermo-optical analyses of systems and materials with highly specific equipment and strong know-how.

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Job description

In this context, a position is offered for 12 to 18 months, depending on the candidate’s qualifications and salary(fixed total budget). He/she will:

  • review the literature on ceramic materials used as CSP solar receivers;
  • study the optical performance of the SiC-TiC samples through:
    • advanced optical characterization, thanks to customized and unique equipment, to allow access to: directional/hemispherical specular/diffuse spectral reflectance at room temperature and up to 500°C (UV-VIS-NIR / IR spectrophotometers 0.25-25 μm), directional/hemispherical emittance at high temperature up to 3000°C (MEDIASE facility with concentrated solar heating from the big solar furnace, pyroreflectometer and radiometer);
    • calculation of their optical properties, such as solar absorptance, thermal emittance, selectivity, solar-to-heat conversion efficiency, using in-house Scilab codes;
  • study the thermal stability and oxidation resistance of the SiC-TiC samples, by:
    • applying static and cyclic aging tests on the samples, thanks to a dedicated programmable electrical furnace (ALTHAIA) under different atmospheres (ambient air, vacuum, dry and humid air);
    • investigating the impact of said aging on their microstructure (SEM, AFM/profilometry), composition (EDS), mechanical properties (nanoindentation) and thermo-optical properties (UV- VIS-NIR and IR spectrophotometry);
  • communicate his/her results through written reports, project deliverables and scientific articles, presentations during progress meetings and conferences;
  • interact with project partners, suppliers and local staff, PhD students, engineers and researchers.

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Location

The candidate will work in Odeillo (solar furnace) and will occasionally travel to the other site of the laboratory in Perpignan (1h30 by car) for material characterization. Travel expenses will be funded.

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Requirements

  • The candidate must have a Master or Engineer degree.
  • A background in Material Science, Chemistry, and/or Optics is required.
  • Although not mandatory, knowledge of Scilab/MATLAB software will be appreciated, as well as a good level of written and spoken English.

Supervisor

Dr. Audrey SOUM-GLAUDE, +33 (0)4 68 30 77 47,

Salary

Depending on qualifications (~1600 – 2000 €)

Starting date

Autumn 2018